NEW YORK (CBS News/CBSNewYork/AP) — The Department of Justice is planning to file criminal corruption charges against New Jersey Sen. Bob Menendez, a law enforcement official told CBS News on Friday.

Sources say the federal corruption charges will be announced in the next couple weeks.

READ MORE: 'Moulin Rouge! The Musical' Wins Big As Broadway Celebrates The 74th Annual Tony Awards

One of the highest ranking Hispanic members in Congress, Menendez was expected to be accused of using his Senate office to promote the interests of Democratic donor Dr. Salomon Melgen, a South Florida eye doctor and close friend.

In response, Menendez insisted that he has always acted lawfully and has fought for the best policies for the people of New Jersey and the U.S. for all of the 23 years he has been in office.

“Let me be very clear — very clear — I have always conducted myself appropriately and in accordance with the law,” Menendez said at a news conference Friday evening.

He said he has been focused from the beginning on “important things,” such as ensuring that victims of Superstorm Sandy have the tools to rebuild, and that Iran never gets its hand on a nuclear weapon.

“I fight for these issues, and the people of our country every single day.” Menendez said. “That’s who I am, and I’m not going anywhere.”

U.S. Attorney General Eric Holder approved prosecutors’ requests to move forward with the charges, CBS News reported. The charges were expected to be filed in the coming weeks.

Menendez characterized Melgen simply as a close personal friend, and said they have spent holidays and exchanged birthday, holiday and wedding presents as friends do.

“Anyone who knows us knows he and his family, and me and my family, have been real friends for more than two decades,” he said.

An earlier statement from a Menendez spokeswoman likewise claimed the senator did nothing wrong.

“As we have said before, we believe all of the senator’s actions have been appropriate and lawful and the facts will ultimately confirm that. Any actions taken by Sen. Menendez or his office have been to appropriately address public policy issues and not for any other reason,” Tricia Enright, Menendez’ communication director, said in a statement.

“As has been reported, the start of this investigation is suspect. We know many false allegations have been made about this matter, allegations that were ultimately publicly discredited. We also know that the official investigation of this matter is ongoing, and therefore cannot address allegations being made anonymously,” Enright added.

Menendez, the former chairman of the Senate Foreign Relations Committee, sponsored legislation with incentives for natural gas vehicle conversions that would benefit Melgen, his biggest political donor to his re-election, an Associated Press investigation found.

At an event in West New York Friday evening, Mayor Felix Roque had nothing but good things to say about the senator, CBS2’s Sonia Rincon reported.

“The senator is an honorable man. He has the pulse on our community, he’s always been there since he was young helping the community,” Roque said.

READ MORE: Police Seize 7 Vans Allegedly Used As Airbnb Rentals In Manhattan

According to CBS2’s Marcia Kramer, during the 2013 election cycle Melgen gave more than $700,000 to Menendez and other Senate Democrats.

Menendez also used Melgen’s private jet for two personal trips to the Dominican Republic, the AP reported. However, after word of the trips became public Menendez paid Melgen $58,000, saying it was an oversight, Kramer reported.

Melgen invested in Gaseous Fuel Systems Corp. of Weston, Florida, and joined its board of directors in early 2010, according to the company’s chief executive and a former company consultant. GFS, as the company is known, designs, manufactures and sells products to convert diesel-fuel fleets to natural gas. The amount of Melgen’s investment is confidential under rules of the Securities and Exchange Commission, but a 2009 document filed with the SEC showed the company required a minimum individual investment at that time of $51,500.

Menendez was a principal supporter of a natural gas bill from 2009 through 2012 that would boost tax credits and grants to truck and heavy vehicle fleets that converted to alternative fuels. The bill stalled in the Senate Finance Committee, and after it was revived in 2012, the NAT GAS Act failed to win the needed 60 votes to advance.

While the bill was under consideration between 2009 and 2011, the former consultant for GFS spent $220,000 lobbying Menendez’s staff and other congressional and federal officials on the act’s provisions as well as other regulatory issues, according to interviews and Senate records.

There is no evidence that Menendez offered direct help or intervened on behalf of the company or Melgen. Instead, the connection between the two men’s interests in natural gas is the latest example of the close symmetry between the senator and his millionaire backer, the Associated Press reported.

David Birdsell, dean of the Baruch College School of Public Affairs, said Menendez is in big trouble if the allegations are true.

“We’re talking about selling influence, we’re talking about improper acceptance of gifts and we’re talking about intervening in U.S. trade negotiations and created issues of another nation,” Birdsell said. “If this turns out to be true it’s going to be very hard for him to escape criminal charges.”

As Rincon reported, that’s because Menendez may also be accused of looking to influence the U.S. Customs Department in a way that would benefit a business of Melgen’s in the Dominican Republic.

The senator has vehemently denied reports that he hired prostitutes in the Dominican Republic. An anonymous tipster told a conservative blog that Melgen reportedly set up the prostitutes for Menendez. As a result, the FBI raided Melgen’s Florida office.

Menendez accused the Cuban government of being behind the prostitution claims.

“Let’s remember how this all started: nameless, faceless accusations that ultimately proved themselves to be false, and early on their was some indications of the Cuban government’s involvement,” Menendez said back in July 2014.

Menendez is Cuban-American and has been a vocal critic of the Cuban government for decades.

The allegations came from three Dominican women who said they’d been paid to have sex with Menendez at a resort in the Caribbean. But in 2013 year the women recanted their story.

“It should be pretty appalling that a foreign government would be engaged in trying to affect an election and or the position of a United States senator. And if that can happen, there are real consequences to our democracy,” Menendez said.

MORE NEWS: Woman Accused Of Telling Black Couple At Brooklyn Dog Park, 'Stay In Your Hood'

(TM and © Copyright 2015 CBS Radio Inc. and its relevant subsidiaries. CBS RADIO and EYE Logo TM and Copyright 2015 CBS Broadcasting Inc. Used under license. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.)